1. Field of the Invention
This invention relates to testing of electrical systems and, more particularly, to devices for arc fault and/or ground fault testing of electrical distribution circuits.
2. Background Information
The common type of circuit breaker used for residential, commercial, and light industrial applications has an electro-mechanical thermal-magnetic trip device to provide an instantaneous trip in response to a short circuit and a delayed trip in response to persistent overcurrent conditions. Some of these circuit breakers include ground fault protection, which trips the ground fault circuit interrupter, (GFCI) in response to a line-to-ground fault, and in some cases, a neutral-to-ground fault. Ground fault protection is provided by an electronic circuit which is set to trip at about 4 to 6 mA of ground fault current for people protection, and at about 30 mA for equipment protection. It is known to incorporate a test circuit in the circuit breaker, which tests at least portions of the electronic ground fault trip circuit. It is also known to test for proper wiring connections. Test circuits for this purpose are commercially available.
Recently, there has been rising interest in also protecting such power distribution circuits, and particularly the branch circuits for homes, commercial and light industrial applications, from arcing faults. Arcing faults are intermittent, high impedance faults, which can be caused for instance by worn or damaged insulation, loose connections, broken conductors and the like. Arcing faults can occur in the permanent wiring, at receptacles, or more likely, in the wiring of loads or extension cords plugged into a receptacle. Because of the intermittent and high impedance nature of arcing faults, they do not generate currents of sufficient instantaneous magnitude or sufficient average current to trigger the thermal-magnetic trip device which provides the short circuit and overcurrent protection.
Various types of arc fault detectors have been developed and/or proposed. Generally, the detectors are of two types. One type responds to the random high frequency noise content of the current waveform generated by an arc. This high frequency noise tends to be attenuated, especially by the presence of filters on some loads, which can be connected to the branch circuit. The other basic type of arc fault detector responds to the step increase in current occurring as the arc is repetitively and randomly struck. Examples of arc fault detectors of the latter type are disclosed in U.S. Pat. Nos. 5,224,006; and 5,691,869.
U.S. Pat. No. 5,459,630 discloses several forms of built-in test circuits for arc fault detectors. In one embodiment, in which the arc fault detector utilizes a coil to sense current, the test circuit adds a capacitor which forms with the impedance of the coil an oscillator generating a waveform with an amplitude which simulates the rapid rise of a step change in current produced by an arc. In another embodiment, the user must repetitively close a switch, which connects a resistor between the line conductor and neutral, to again generate large amplitude pulses.
While the built-in arc fault and ground fault testers test the response of the electronic circuits to simulated conditions, they do not necessarily indicate whether the device will adequately respond in a real installation. One difficulty is that the circuit breaker containing the detectors is located at a load center together with the circuit breakers for other circuits in the installation. However, the fault condition can occur anywhere downstream and can be further distanced from the circuit breaker and detectors by an extension cord. The wiring, and particularly the extension cord, can insert considerable resistance between the fault and the detector, which attenuates the signal sensed by the detector. When the effects of this resistance are combined with the low amplitude of the currents generated by these faults, the detectors may not have sufficient sensitivity to detect remote faults. Another problem can arise when a receptacle is not connected as intended.
Detection of an arcing fault is complicated by the fact that some normal loads can produce waveforms similar to arcing faults. Arc fault detectors attempt to distinguish over such phenomena to minimize nuisance faults. The task is further complicated by the fact that, as mentioned above, arcing faults tend to be smaller in amplitude than dead faults.
With the introduction of arc fault circuit interrupter (AFCI) devices, such as arc fault circuit breakers, there exists the need for an apparatus for determining the location of problems within electrical wiring. There is a need for a troubleshooting tool to permit users, such as electricians, to identify and locate arc fault, ground fault and other system wiring problems that may be encountered during and after the installation of the AFCI device.
There is also a need for such test devices, which are flexible, simple, safe and economical.
These needs and others are met by the present invention, which provides a testing device for detecting and locating an arcing fault having one or more characteristics in an electrical system. Furthermore, the testing device may be employed to locate electrical conductors and/or to detect one or more faults in the electrical system. Also, the testing device may be used in combination with a pulsing device, which produces a periodic arcing signal to cause one or more of the arcing fault characteristics, in order to provide a testing system for detecting and locating an arcing fault in the electrical system.
As one aspect of the invention, a testing device for detecting and locating an arcing fault in an electrical system comprises: means for detecting at least one of a plurality of characteristics of the arcing fault proximate the arcing fault and outputting a responsive signal; and means for annunciating the responsive signal when the means for detecting is proximate the arcing fault, in order to locate the arcing fault in the electrical system.
One of the characteristics may be a radio frequency signal, and the means for detecting may include an antenna for receiving the radio frequency signal and a radio frequency detector for detecting the received radio frequency signal.
One of the characteristics may be an ultrasonic sound, and the means for detecting may include a pick-up coil for receiving the ultrasonic sound and outputting a corresponding electrical signal, and means for detecting the electrical signal.
One of the characteristics may be an audible sound, and the means for detecting may include a pick-up coil for receiving the audible sound and outputting a corresponding electrical signal, and means for detecting the electrical signal.
As another aspect of the invention, a testing device for detecting and locating an arcing fault in an electrical system comprises: means for locating a plurality of the electrical conductors of the electrical system; means for detecting at least one of a plurality of characteristics of the arcing fault proximate one of the electrical conductors and outputting a responsive signal; and means for annunciating the responsive signal when the means for detecting is proximate the arcing fault.
As another aspect of the invention, a testing device for detecting faults in an electrical system, and for detecting and locating an arcing fault in the electrical system comprises: means for testing the electrical system to detect at least one fault in the electrical system; means for detecting at least one of a plurality of characteristics of the arcing fault proximate the arcing fault and outputting a responsive signal; and means for annunciating the responsive signal when the means for detecting is proximate the arcing fault.
The means for testing may include means for conducting a ground fault test of the electrical system. The means for conducting a ground fault test may include first means for engaging a line conductor of the electrical system, second means for engaging a ground conductor of the electrical system; and means for adjusting a load between the first and second means, in order to provide between about 6 to 100 mA of leakage current in the line conductor and the ground conductor.
As another aspect of the invention, a testing system for detecting and locating an arcing fault in an electrical system comprises: means for producing an arcing signal to cause at least one of a plurality of characteristics of the arcing fault; and a testing device comprising: means for detecting the at least one of the characteristics of the arcing fault proximate the arcing fault and outputting a responsive signal, and means for annunciating the responsive signal when the means for detecting is proximate the arcing fault.